1. Field of the Invention
The present invention pertains to a screw type press or extruder for extracting liquid from oilseeds, grain mash and raw agricultural products, and for extruding and cooking various types of such products.
2. Description of the Prior Art
In processing oilseed products, and extraction of liquids from other raw or processed agricultural products it is known to use mechanical screw or auger type presses or extruders for performing liquid extraction and for preparing the material for further treatment or storage.
A number of problems have been encountered with known types of screw extruders including the inability to handle material with high liquid content, jamming or clogging of the material in the extruder due to hardening and resistence to flow of the compacted material as it reaches the discharge end, and mechanical complexity necessitating expensive manufacture and repair.
For example, some known screw type presses or extruders are adapted to have an elongated screw mounted in a tubular housing and supported at one or both ends by bearings. The various applications to which screw type extruders are applied quite often produce a considerable amount of heat and pressure on the material which results in damage to the bearings and other associated drive mechanism in the flow path of the material. Moreover, in the extrusion and cooking of grain mashes and oilseed protein products such as corn, soybeans, cottonseed and the like with screw type extruders a hard, tough semi-plastic mass is produced which can overload or jam the extruder mechanism resulting in the shut down of the entire process system in connection with which the extruder is being used. Prior art screw type extruders have proven to be difficult to disassemble and clean making them further unattractive for use in complex processing systems such as the production of alcohol in large quantities from grain products.
Another longstanding problem associated with screw type extruders pertains to proper control of the progressive increase in pressure exerted on the material as it is conveyed through the apparatus to perform liquid extraction and progressively compact and expel the material at the discharge end in a desired condition suitable for transportation and storage or further processing.
A still further problem in the art of mechanical screw type extruder-cookers pertains to proper control of the heating of the material durong start up and during steady state operation.
Known designs of screw type extruders also, generally speaking, require a considerable amount of mechanical power and must be operated at relatively high rotative speeds for processing oilseed products in the so called cooking operations whereby the material being processed is compacted and heated by external means or by friction generated in the extruder itself.
Known types of screw extruder-cookers are also designed to operate with partially processed products for removing a high percentage of liquid. Such equipment is not suitable or cost effective for use in connection with alcohol production processes for producing gasohol, for example.
Known screw type extruders for processing oilseed products, grain used in alcohol production, and other viscous plastic materials have generally been designed for specific uses in connection with only one type of material and accordingly, heretofore known equipment has not enjoyed the versatility that the improvements represented by the present invention provide.